Pressure sensors find a variety of industrial and commercial applications, such as automotive vehicles, hydraulic systems, engine testing, and so forth. Gage pressure sensors, vacuum pressure sensors, differential pressure sensors, absolute pressure sensors and barometric pressure sensors, for example, represent different types of pressure sensors widely accepted in industry today. Depending on particular aspects of their characteristics, each one of these sensor types can be used for a different application. Such devices can be adapted for use for, example, with high-accuracy pressure measurements in hostile media, such as corrosive liquids and gases and hence, need to be robust, reliable while maintaining a long lifetime with greater corrosion resistance.
Some pressure sensors use dry air as the pressure media. Media other than dry air often produces adverse effects, however, on the sensor's performance and long-term stability. For example, a known compensated semiconductor pressure sensor has been adapted for use as a fluid media compatible integrated pressure sensor. Such a device generally includes a sensor capsule, a semiconductor die, a diaphragm region responsive to applied pressure, an outer frame region, a stress isolation region to couple the rim region to the outer frame region, and a silicon cap bonded to the outer frame region of the semiconductor die to cover the diaphragm region. Such a sensor, however, lacks the ability to interact properly with fluid media as well as gaseous media and also faces drawbacks such as corrosion.
Another type of known pressure sensor is based on the formation of a topside reference cavity for a pressure sensor. Such a device includes a silicon diaphragm having bottom and top surface and media being applied to the bottom surface. The cap is glass such as Pyrex and is attached by anodic bonding. The media pressure is sensed by the pressure sensor in relation to the reference pressure sealed on the topside of the diaphragm. This device, however, faces some major problems like output signal drift.
A further known semiconductor pressure sensor includes a first semiconductor layer that forms a base, an insulating layer formed on the first semiconductor layer, a second semiconductor layer formed on the insulating layer and a diaphragm portion constituting a pressure-sensitive region. The methods of formation of the layers for such a device are difficult to use in harsh media such as fluid media or gaseous media.
Pressure sensors should be compatible with fluid media as well as gaseous media if such devices are to work efficiently and with the greatest possible accuracy. Such pressure sensors should ideally be able to operate with improved thermal expansion matching and improved signal output drift. Therefore, there is a need for a pressure sensor that overcomes the aforementioned drawbacks.